Well definitely don't force it. Get under the hood or the car itself and inspect the shift linkage to see what the problem is. If you had specified the type of car or trans I could be of more help. It probably just bound.
If the car has been sitting for a long time, oil the linkage and let the oil penetrate the metal for awhile and try to move it. If the linkage suddenly got stuck, check for binding or a foreign object lodged in the linkage.
If you are having this type of problem then you will need to get to your transmission first. Then you can tell what the problem is and be able to fix it.